A ring of muscle surrounding and serving to guard or close an opening or tube, such as the anus or the openings of the stomach.
- ‘This smooth muscle is the involuntary sphincter of the posterior urethra in the male.’
- ‘Anal manometry is performed to assess the anal sphincter, pelvic floor, and associated nerves.’
- ‘It is girdled by the external anal sphincter, a striated muscle structure that is part of the pelvic floor musculature.’
- ‘This rapidly closes the duodenal sphincter to contain the stomach contents.’
- ‘Then your brain tells your pelvic floor muscles to relax and your sphincter (the opening at the neck of your bladder) to open.’
Late 16th century: via Latin from Greek sphinktēr, from sphingein bind tight.